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C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring

C07C29/132—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of an oxygen containing functional group

C07C29/136—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of an oxygen containing functional group of >C=O containing groups, e.g. —COOH

C07C29/147—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of an oxygen containing functional group of >C=O containing groups, e.g. —COOH of carboxylic acids or derivatives thereof

C07C29/149—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of an oxygen containing functional group of >C=O containing groups, e.g. —COOH of carboxylic acids or derivatives thereof with hydrogen or hydrogen-containing gases

C—CHEMISTRY; METALLURGY

C07—ORGANIC CHEMISTRY

C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS

C07C2601/00—Systems containing only non-condensed rings

C07C2601/12—Systems containing only non-condensed rings with a six-membered ring

C07C2601/14—The ring being saturated

Abstract

The invention relates to a method for producing hexanediol-1,6 from a carboxylic acid mixture containing adipic acid, 6-hydroxycaproic acid and small amounts of 1,4-cyclohexanediols, said mixture being obtained as a by-product of the oxidation of cyclohexane to form cyclohexanon/cyclohexanol with oxygen or gases containing oxygen and through the water-extraction of the reaction mixture, by means of esterification of the acids and hydrogenation. The method comprises the following steps: a) converting the mono- and dicarboxylic acids contained in the aqueous dicarboxylic acid mixture to the corresponding carboxylic acid esters with a low-molecular alcohol; b) liberating the resulting esterification mixture from excess alcohol and light-boiling substances in a first distillation stage; c) separating the bottom product into an ester fraction which is essentially free of 1,4-cyclohexanediols and a fraction containing at least the majority of the 1,4-cyclohexanediols; d) hydrogenating the ester fraction which is essentially free of 1,4-cyclohexanediols with a catalyst; and e) extracting hexanediol-1,6 from the discharge from the hydrogenation using a method known per se, in a pure distillation step. According to the invention, an aqueous dicarboxylic acid containing more than 20 ppm cobalt and more than 40 ppm phosphorus is used in the form of phosphate and this aqueous dicarboxylic acid mixture is passed over a cation exchanger and after the esterification in accordance with step (a), over an anion exchanger.

e) in einer Reindestillationsstufe aus dem Hydrieraustrag in an sich bekannter Weise Hexandiol-1,6 gewinnt, wobei man erfindungsgemäß ein wäßriges Dicarbonsäuregemisch verwendet, das mehr als 20 ppm Kobalt und mehr als 40 ppm Phosphor in Form von Phosphat enthält und daß man dieses wäßrige Dicarbonsäuregemisch über einen Kationenaustauscher und nach der Veresterung gemäß Stufe (a) über einen Anionenaustauscher leitet. e) in a purifying distillation stage from the hydrogenation effluent in a known manner, 1,6-hexanediol, wins being used according to the invention is an aqueous dicarboxylic acid mixture, which contains more than 20 ppm of cobalt and more than 40 ppm of phosphorus in the form of phosphate and in that this aqueous passes dicarboxylic acid mixture over a cation exchanger and, after the esterification of stage (a) over an anion exchanger.

Obwohl die Verwendung von Ionenaustauschern zur Entfernung von Kationen bzw. Anionen allgemeiner Stand der Technik ist, war es überraschend, daß bei dem erfindungsgemäßen Verfahren keine uner wünschte Nebenreaktionen bei der zwischen dem Kationenaustauscher und dem Anionenaustauscher befindlichen Entwässerung eintraten. Although the use of ion exchange resins to remove cations or anions is general prior art, it was surprising that in the present process no unwanted side reactions in the wish situated between the cation exchanger and the anion exchanger drainage occurred.Im sauren Kationenaustauscher wird nämlich das Phosphat in Phosphorsäure umgewandelt, so daß damit gerechnet werden mußte, daß bei der destillativen Entwässerung der mit dem Kationen austauscher behandelten Carbonsäurelösung sauer katalysierte Reaktionen der 6-Hydroxycapronsäure auftreten würden, wie Eliminierung der Hydroxylgruppe oder Polyesterbildung. In the acidic cation exchanger, the phosphate in the phosphoric acid that is converted, so that had to be expected that acid-catalyzed reactions of the 6-hydroxycaproic acid would occur during the distillative dewatering of the exchanger with the cation-treated carboxylic acid solution, such as elimination of the hydroxyl or polyester formation.Beides ist jedoch nicht der Fall. But neither is the case.Die Bildung der Phosphorsäure hat sogar den Vorteil, daß sie als Veresterungskatalysator dienen kann und die Menge der zuzusetzenden Schwefelsäure als Ver esterungskatalysator verringert werden kann. The formation of the phosphoric acid has even the advantage that it can serve as an esterification catalyst and the amount of sulfuric acid to be added can be reduced esterungskatalysator as Ver.

Das erfindungsgemäße Verfahren ist abgesehen von der Behandlung des wäßrigen Carbonsäuregemischs mit dem Kationenaustauscher und des Veresterungsreaktionsgemisches mit dem Anionenaustauscher in allen Einzelheiten in WO 97/31882 beschrieben, so daß auf diese Schrift ausdrücklich Bezug genommen wird. The inventive method is apart from the treatment of the aqueous acid mixture with the cation exchanger and of the esterification reaction mixture with the anion exchanger in detail in WO 97/31882, described so that reference is expressly made to this document.Sämtliche dort gemach ten Angaben sollen auch hier ohne irgendwelche Beschränkungen gelten. All gemach th there information should also apply here without any restrictions.

Die Abtrennung des Wassers kann so erfolgen, daß das Wasser über wiegend säurefrei erhalten wird, oder man kann die in der DCL enthaltenen niederen Monocarbonsäuren - im wesentlichen Ameisen säure - zum größten Teil mit dem Wasser abdestillieren, damit diese in der Veresterung keinen Veresterungsalkohol binden. The removal of water can be such that the water is obtained via weighing acid-free, or can be the lower monocarboxylic acids present in the DCS - acid substantially ants - distilled off for the most part with the water, so that they do not bind any esterification in the esterification.